There are about 26 bones in the human foot (about 28 if you include the sesamoid bones at the base of the big toe). These are: 1) the talus, which connects to the tibia and fibula at the ankle; 2) the calcaneus, which forms the heel; 3) the navicular, cuboid, and three cuneiforms (medial, intermediate, and lateral), which form the middle of the foot; 4) the five metatarsals, which radiate out to the toes; and 5) the 14 phalanges (2-3-3-3-3), which form the toes.
The joint named “ankle” is made up of the tibia, the fibula, and the talus. Below the talus is another joint called the “below the talus joint” or, in another language, the subtalar joint. That joint between the talus and calcaneus is intricately inseparable from the action of the midfoot and rearfoot joints.
Charcot neuroarthropathy (CN) is defined by a bone and/or joint deformity in limbs that have lost sensory innervation. The incidence is very high in diabetic patients with peripheral neuropathy. Currently, the pathogenesis of CN is largely unknown. This is often reflected in that diabetic patients with CN present challenging surgical candidates secondary to diabetes-related complications.
CN is a progressive disorder believed to result from a disturbance in pain and sensation as a result of peripheral neuropathy. Originally described as a complication of syphilitic neuropathy, the Charcot foot and ankle in the last decade has been most commonly associated and treated in patients with uncontrolled diabetes mellitus and dense peripheral neuropathy. The true etiology and nature of this debilitating condition is still unknown, and the treatment is variable and patient-dependent. Historically, foot and ankle deformities as a result of CN were treated with immobilization, total contact casting and, later, with accommodative footwear or bracing. Unfortunately, the evidence supporting non-operative treatment for the Charcot foot is equivocal. The increased risk of amputation in the non-operative treatment of CN should alert the treating physician to use caution and close monitoring in the presence of a severe deformity, fracture/dislocation, instability, and/or ulceration. Currently, the literature has shown variable protocols, techniques, and outcomes for surgical reconstruction of these complex and debilitating deformities, raising great concerns on the treatment options for the Charcot foot and ankle.
The presence of ulceration, severe osseous deformity, poor bone quality, neuropathy, immune deficiency, obesity and multiple co-morbidities commonly seen in this patient population limit the use of traditional internal fixation to achieve a successful outcome. The risk of surgical infection is increased in diabetics due to their impaired immune system. In the presence of ulceration with an underlying bony prominence, this risk of infection and future amputation is high, and the ability to utilize internal fixation alone is limited. Accordingly, CN involving severe deformity, instability, ulceration, and/or infection of the foot and/or ankle poses difficulty in achieving limb salvage. When the surgeon is faced with this clinical scenario, limb salvage is often plausible through a rationale approach that, in various treatments, incorporates arthrodesis of affected joints to correct the deformity, plastic soft tissue reconstruction for wound closure, and application of an external fixation device.
Generally, arthrodesis has been used to artificially induce joint ossification between two bones via surgery. A bone graft can be created between the two bones using a bone from elsewhere in the person's body (autograft) or using donor bone (allograft) from a bone bank.
Bone autograft is generally preferred by surgeons because, as well as eliminating the risks associated with allografts, bone autograft contains native bone-forming cells (osteoblasts), so the graft actually forms new bone itself (osteoinductive); it acts as a matrix or scaffold to new bone growing from the bones being bridged (osteoconductive). The main drawback of bone autograft is the limited supply available for harvest.
Bone allograft has the advantage of being available in far larger quantities than autograft; however, the treatment process the bone goes through following harvest, which usually involves deep-freezing and may also involve demineralization, irradiation and/or freeze-drying, kills living bone or bone marrow cells. This significantly reduces the immunogenicity (risk of graft rejection) such that no anti-rejection drugs are needed and, combined with appropriate donor screening practices, these processing and preservation practices can significantly reduce the risk of disease transmission. In spite of all of this processing, cancellous allograft bone retains its osteoconductive properties. Furthermore, certain processing practices have been shown to also retain the acid-stable osteoinductive proteins in cortical bone grafts so that many bone allografts can be considered both osteoconductive and osteoinductive.
Likewise, a variety of synthetic bone substitutes are commercially available. These are usually hydroxyapatite-based granules formed into a coralline or trabecular structure to mimic the structure of cancellous bone. Such materials can include, for example, bone cement, demineralized bone matrix, hydroxyapatite and calcium phosphate materials.
Many of the above procedures are costly, require extensive healing and are not always successful; accordingly, the art field is in search of novel and improved processes and apparatuses for treating such conditions.
In view of the foregoing, it is an object of the present invention to provide an apparatus for compressing and stabilizing a patient's foot, ankle, and/or lower extremity, particularly those conditions in which internal fixation alone is insufficient. Hence, various embodiments of the present invention include external fixation in combination with internal fixation to create compression across a larger linear gap. Such combination systems and methods may be advantageous for repairing diseased bone in which large defects are present such as, for example, CN.